The present invention relates generally to direct current (d.c.) motor regulators and more specifically to regulators having current and speed feedback loops for the regulation of motor operation.
In the field of motor regulation it is well known to provide both speed control and current limit; that is, regulation in which the speed of the motor will be maintained at a desired value until such time as the motor reaches a point at which the current exceeds a prescribed limit. When the current limit is reached, another portion of the regulator will become effective to prevent the motor current from further increase. The theoretically perfect speed/current curve achieved by a motor is one in which the speed remains absolutely constant until such time as the current limit is reached at which time there is no further increase in speed and the current will remain constant even though the speed may decrease to zero. As a practical matter, such a perfect curve is never achieved partially because of imperfections in equipment and components and partially because there is normally some form of interaction between the current limiting and speed control portions of the regulator.
It is also recognized by those skilled in the art that a closely regulated d.c. motor, as will be more fully described in the detailed specification which follows, can become unstable when rapid regulation changes are required. This is because certain of the circuit components used in the control are inherently frequency responsive and the motorload itself, when viewed as a system, is also responsive to frequency.
Numerous schemes for speed control to achieve both adequate regulation and stability have been devised. These schemes are generally complex and if designed to be useful over a range of motors have required a plurality of adjustments due largely to the fact that the frequency responsive elements including the motor system itself do exist. For these reasons it is generally desirable to provide a relatively high gain at low frequencies and a low gain at high frequencies.